Crude oil production from oil in subterranean reservoirs may involve use of various flooding methods as the natural forces that are used in the “primary recovery” process become depleted. A large portion of the crude oil may have to be driven out of the formation in “secondary” or “tertiary” recovery processes. In addition, some reservoirs may not have sufficient natural forces for oil production even by primary recovery processes. The production of crude oil using such flooding methods is one example of enhanced oil recovery process.
One trend in the petroleum industry now is to plan exploitation of the oil field at the beginning of the project. Injecting a displacing fluid or gas may begin early, long before the complete depletion of the field by primary recovery processes. Methods for improving displacement efficiency or sweep efficiency may be used at the very beginning of the first injection of a displacing fluid or gas, rather than under secondary and tertiary recovery conditions.
The least expensive and easiest method of flooding a subterranean reservoir 2 for the production of crude oil is by injecting a liquid or a gas into the well to force the oil to the surface. Water flooding is the most widely used fluid. However, water does not readily displace oil because of the immiscibility of water and oil and/or the high interfacial tension between the two liquids.
The addition of chemicals to modify the properties of the flooding liquid is well known in the art. Surfactants are one class of chemical compounds that have been used in aqueous media for enhanced oil recovery. Surfactants have been found to effectively lower the interfacial tension between oil and water and enabling the oil droplets to flow more easily through the channels of the reservoir.
Alkylaryl sulfonates have been used as surfactants for enhanced oil recovery. They have been used in surfactant flooding, alone, or in conjunction with co-surfactants and/or sacrificial agents. Alkylaryl sulfonates are generally used not only because they are able to lower the interfacial tension between oil and water, but also because when used in conjunction with varying amounts of sodium chloride they exhibit different phase behavior. At low salinity, alkylaryl sulfonates can have a tendency to stay in the aqueous phase, but at high salinity they tend to stay in the oil phase. Around mid-point salinity, a micro-emulsion forms in which appreciable amounts of oil and brine are in the micro-emulsion phase. It is at this mid-point salinity that the surfactant exhibits high oil recovery potential. The salinity of the water in subterranean hydrocarbon reservoirs may vary a great deal, for example, the Minas oil field in Indonesia has total dissolved salts of between 0.2 and 0.3 weight percent. Other reservoirs may have salinities as high as or higher than 2.0 percent sodium chloride and over 0.5 percent calcium chloride and magnesium chloride. It is desirable to optimize the alkylaryl sulfonates for surfactant flooding for enhanced oil recovery for a particular reservoir by determining the interfacial tension of the reservoir oil in an aqueous brine solution containing the alkylaryl sulfonates which matches the salinity of the reservoir water.
Generally, pure alkylaryl sulfonates, that is, those having a narrow range of molecular weights, are useful for recovery of light crude oils. Such alkylaryl sulfonates have been less useful for enhancing oil recovery of crude oils containing high wax content. Alkylaryl sulfonates having a broad spectrum of carbon chain lengths in the alkyl group are more desirable for use to recover waxy crude oils.
A number of patents and patent applications have discussed methods for enhanced oil recovery using surfactant flooding. In addition to the use of surfactants, there are a number of patent and patent applications discussing the use of co-surfactants and sacrificial agents for enhanced oil recovery.
EP 0 111 354 B1 discloses the use of alkylxylene sulfonate compounds derived from alkyl meta- and para-xylenes in methods for displacing oil from reservoirs of relatively higher salinities than those to which the conventional alkyl ortho-xylene sulfonate compounds are limited.
EP 0 148 517 B1 discloses olefin sulfonate compositions comprising an aqueous solution containing 15 to 35 weight percent of a blend of C12-C22 linear alpha-olefin and an alkylaryl sulfonate wherein the aryl group is benzene, toluene or xylene. The compositions are used in foam drive processes for enhanced oil recovery.
EP 0 158 486 B1 discloses the use of polyalkyl aromatic sulfonates, particularly dialkyl aromatic sulfonates in steam recovery methods for enhancing oil recovery. The increase of the ratio of para-isomer to meta-isomer results in a significantly more hydrolytically, thermally stable surfactant under steam recovery operating conditions.
EP 0 413 374 B1 discloses the use of alkylxylene sulfonates and a glycol for enhanced oil recovery. The alkyl group containing 8 to 30 carbon atoms is attached to the aromatic ring from its 2-position to its mid-position. The glycol is used as a sacrificial agent.
GB 2 138 866 A discloses a micellar slug for use in the recovery of oil consisting essentially of a hydrocarbon, an aqueous medium, a surfactant and a co-surfactant. The surfactant containing, as essential constituents, an internal olefin sulfonate having 10 to 26 carbon atoms and at least one ethoxylate. The micellar slug has an improved salinity tolerance and hard-water resistance and is capable of forming micro-emulsions having low interfacial tension and good stability.
U.S. Pat. No. 3,601,198 discloses the use of oil-soluble anionic surface-active agents or detergents, such as sulfonates, petroleum and synthetic, for a hydraulic fracturing operation. The synthetic sulfonates are alkaline earth metal salts of high molecular weight sulfonic acids and are produced using aromatics, such as benzene, toluene, xylene and naphthalene. The molecular weights of the sulfonates are in the range between 300 and about 750.
U.S. Pat. No. 4,005,749 discloses the use of polyalkylene oxides as sacrificial agents prior to surfactant flooding in enhanced oil recovery process. The polyalkylene oxides have molecular weights of at least 1,200. The surfactant flood is an aqueous slug containing a surfactant exhibiting a lower molecular weight than that of the polyalkylene oxides. The sacrificial agent may also be used along with the surfactant flooding, but its concentration is lower than when used as a sacrificial agent.
U.S. Pat. No. 4,217,958 discloses the use of sacrificial agents, polybasic carboxylic acid or their water soluble salts, in admixture with a chemical oil recovery agent, such as a surfactant, a polymer, and/or a micellar dispersion to reduce the adsorption of surfactants and/or the polymers on reservoir rock.
U.S. Pat. No. 4,452,708 discloses an oil recovery method using a particular class of alkylaryl sulfonate surfactants. The surfactants are derived from an extracted aromatic feedstock consisting essentially of benzene, toluene, xylene and lesser amounts of alkylbenzene alkylated with linear alpha-olefins to favor second-carbon attachment. The sulfonates have high oil solubilization parameters and their phase behavior is substantially independent of temperature over 120° F.-250° F.
U.S. Pat. No. 4,476,929 discloses the use of co-surfactants, a sulfoxide, having a maximum of 14 carbon atoms, in surfactant systems for enhanced oil recovery processes. The preferred surfactant is a petroleum sulfonate having average equivalent weights in the range of about 325 to 500.
U.S. Pat. No. 4,452,308 discloses the use of polyalkylene glycols or copolymers thereof having molecular weights between 100 and 1,200 with chemical flooding. The concentration of the polyalkylene glycols used is 0.01-0.5 weight percent. The preferred polyalkylene glycols are polyethylene and polypropylene glycols.
U.S. Pat. No. 4,589,489 discloses the use of polyalkylene glycols or their copolymers for surfactant flooding or for preflushing. It is preferred to use polyethylene glycol having a molecular weight of from 800 to about 1,100. The concentration used is dependent on the subterranean formation, for example, between 1-100 kilograms per cubic meter.
U.S. Pat. No. 4,608,204 discloses a process for the preparation of a low viscosity aqueous alkyltoluene or alkylxylene sulfonate with the addition of sodium chloride during neutralization or after neutralization. Such low viscosity sulfonates are useful as surfactants in enhanced oil recovery processes. When xylene is employed, a mixture of the three isomers, ortho-, meta- and para-, are preferred.
U.S. Pat. No. 4,690,785 discloses low water neutralization energy-saving process to produce highly active alkylaryl sulfonate by combining an alkylaryl sulfonic acid with a salt-forming base, and utilizing the heat generated during the neutralization reaction to drive off the water present in the reaction mixture. The resulting free flowing alkylaryl sulfonate powder is at least 90 percent active. When dissolved in water, the powdered product will have a pH of about 4.6 to about 11.5, usually about 7 or about 8.
U.S. Pat. No. 4,873,025 discloses compositions comprising alkylxylene sulfonates in which a substantial portion of the alkylxylene sulfonate fraction has C6-C20 substituents, positioned directly opposite to the sulfonate moiety. Such compositions are derived from para-xylene or isomer mixtures comprising substantially para-xylene. These alkylxylene sulfonates are useful as surfactants, particularly in enhanced oil recovery techniques.
U.S. Pat. No. 4,932,473 discloses a process for enhanced oil recovery employing one or more alkyltoluene sulfonates in a saline aqueous solution. The improvement comprises including into the said solutions one or more alkylpolysaccharide surfactants for enhancing the solubility of the alkyltoluene sulfonate. The composition enhances calcium and sodium ion tolerance of the alkyltoluene sulfonates.
U.S. Pat. No. 6,022,834 discloses an improved alkali surfactant flood process with ultra-low interfacial tension. The surfactant system contains (1) a mixture of anionic surfactants; (2) solvent(s); (3) a strong base; and (4) optionally, a nonionic surfactant or mixtures of nonionic surfactants or sulfates or carboxylates of these nonionic surfactants. The anionic surfactants are sulfonates derived from alkylbenzene, alkylnaphthalene, alkyltoluene or alkylxylene. The alkyl group consists of between about C4 and about C24.
U.S. Pat. No. 6,043,391 discloses new anionic surfactants and their method of preparation by simultaneously sulfonating and alkylating an aromatic hydrocarbon. The one-step preparation process involves sulfonating an alpha-olefin with SO3, followed by repeated hydrolysis and dehydration with water which results in the formation of an alkene sulfonic acid. This strong acid is then used to alkylate aromatic compounds. Additional strong acid catalyst is beneficial to obtain useful yields of the final product.
U.S. Pat. No. 6,269,881 discloses an oil recovery process using a particular class of alkylaryl sulfonates derived from an alpha-olefin stream having a broad distribution of even carbon numbers ranging from 12 to 58. The aromatic hydrocarbons used to produce the alkylaryl sulfonates may be benzene, toluene, xylene or mixtures thereof. The surfactant has ultra low interfacial tension with waxy crude oils.
WO 01/98432 A2 discloses a surfactant blend for lowering the interfacial tension between oil and aqueous fluid for enhanced oil recovery. The blend comprises at least one synthetic polyisobutylene and at least one surfactant consisting of sulfonate surfactants, alcohols and non-ionic surfactants.
A general treatise on enhanced oil recovery is Basic Concepts in Enhanced Oil Recovery Processes edited by M. Baviere (published for SCI by Elsevier Applied Science, London and New York, 1991).